Just lost a game when they spawned in the empire right next to mine. Also i ended up being an AI's vassal that game, which kinda sucked. Was behind in tech and military all game, and constantly had resource shortages. I need to try something different, clearly.

Also my idiot AI Overlord and his federation decided that the swarm's arrival was the perfect time to declare war on the other big federation in the galaxy. *sigh*

Yeah one thing about the end game crisis events is that it tend to become a bit to much you vs the end game event. The AI do not really rally to fight these events. Hopefully they will improve on that a bit more.

The Prethoryn swarm are actually pretty easy if you have your fleets specced correctly.

They rely almost completely on missiles and strike craft so if you build a bunch of battleships with extreme range weapons and have a bunch of point defenses on everything else then you can take down fleets with considerably higher calculated strengths than your own.

Plus once you bomb all their infested planets the event immediately ends.